Electrical terminals for semiconductor power modules as IGBTs (Insulated Bipolar Gate transistors) power modules switch currents up to a few thousand Amperes. The electric connection from the outer contacts of the module to the chips is provided by metal conductors which are referred to as terminals. The terminals have one electrical contact for the outer contact, which is fixed at the housing. FIG. 1 shows a known electrical terminal 10. The electrical terminal 10 includes a primary electrical contact 2, a secondary electrical contact 3, and a connection element 4, which electrically connects the first and secondary electrical contacts 2, 3. The connection element 4 is arranged in a plane and includes a plate-like region 41 with a deflection means 44. The deflection means 44 includes a first section 45, a second section 46 and a third section 47, which is arranged between the first and second sections 45, 46. The first section 45 is separated from the third section 47 by a first cut 451, except for a first joint 454 acting as a first hinge which includes a first pivot 452. The second section 46 is correspondingly separated from the third section 47 by a second cut 461, except for a second joint 464 acting as a second hinge which includes a second pivot 462. The first and second joints 454, 464 have a reduced cross-section as compared to the third section 47 between these joints 454, 464 in order to improve the bending capability of the pivots 452, 462. By this arrangement, a current path 5 (dotted line in FIG. 1) is formed from the primary electrical contact 2 through the first section 45, the first joint 454, the third section 47, the second joint 464, the second section 46, and the secondary electrical contact 3. The top part of the terminal 10 is fixed with the module housing so that the primary electrical contact 2 sticks out of the housing. The secondary electrical contact 3, which is arranged within the semiconductor module, is soldered to a metalized ceramic substrate for electrically contacting a semiconductor chip. In cases of modules with a number of parallel connected IGBTs, such a terminal 10 includes two secondary electrical contacts 3 (a first and second secondary electrical contact 31, 32), which are electrically connected to the primary electrical contact 2 by a common first section 45 and a mirror-inverted arrangement of the first joints 454, the third sections 47, the second joints 464, the second sections 46, and the corresponding first or second secondary electrical contacts 31, 32.
During operation of the power module, the module undergoes temperature changes due to currents, which lead to self-heating of the terminals, especially at high currents or fast current changes, which can occur during switching processes. This leads to a cyclic expansion of the module housing. As a result, the primary electrical contact 2 is displaced with respect to the secondary electrical contact 3, and forces are applied to the terminal 10, which lead to a dilatation or compression of the deflection means 44. To achieve this movement, the terminal bends at the first and second pivots 452, 462, thereby creating normal forces FN (shown by the arrow in FIG. 1) and shear forces FS on the secondary electrical contact 3 (31, 32). These shear forces FS lead to solder deformation at the contact between the secondary electrical contact 3 (31, 32) and the substrate, and finally lead to a module failure.
In order to keep the temperature rise of the terminals 10 low, the electric resistance of the plate-like region 41 has to be low, which can be achieved by plates with a large cross-section. On the other hand, in order not to have high forces occurring in the module when it is expanded by temperature changes, high mechanical flexibility of the terminal is required, which can be achieved by plates with a small width, i.e. a small cross-section.
FIG. 2 shows an electrical terminal 10 with two secondary electrical contacts 31, 32, in each of which shear forces FS are created. Such a plurality of secondary electrical contacts are used for parallel connecting a plurality of chips.